C ha p te r 1 zyxwvutsrqponmlkjihgfedcbaZYXW Recent Advances in Chemistry of Enzymatic Browning zyxwvutsrqponmlkjihgfedcbaZYXWVU An Overview John R. Whitaker 1 and Chang Y. Lee 2 1 Department of Food Science and Technology, University of California, Davis, CA 95616 2 Department of Food Science and Technology, Cornell University, Geneva, NY 14456 Polyphenol oxidase (PPO) is important in the beneficial coloration of some of our foods, such as prunes, dark raisins and teas. However, in most cases, PPO is the most damaging of enzymes in color deterioration (browning) of plant foods, with resulting losses of up to 50% for tropical fruits and others. Preventing PPO activity in postharvest fruits and vegetables has enormous economic and quality benefits, but current prevention methods are not ideal. Through an understanding of the structure and mechanism of action of PPO, and the chemistry of enzymatic browning, better prevention methods can be used, including decrease in PPO biosynthesiszyxwvutsrqponmlkjihgfedcbaZ in vivo by the antisense RNA method. PPO can be used commercially in the biosynthesis of L-DOPA for pharmaceutical uses and for production of other polymeric products. PPO is stable in water-immiscible organic solvents, facilitating specific oxidation reactions with water- insoluble organic compounds. Melanins for use as sun blockers can be produced readily by PPO genetically engineered into Escherichia coli. Polyphenol oxidase (PPO) is a generic term for the group of enzymes that catalyze the oxidation of phenolic compounds to produce brown color on cut surfaces of fruits and vegetables. Based on the substrate specificity, Enzyme Nomenclature (i) has designated monophenol monooxygenase, cresolase or tyrosinase as EC 1.14.18.1, diphenol oxidase, catechol oxidase or diphenol oxygen oxidoreductase as EC 1.10.3.2, and laccase or p-diphenol oxygen oxidoreductase as EC 1.10.3.1. PPO is found in animals, plants and microorganisms. The role of PPO in animals is largely one of protection (pigmentation of skin, for example), while the role of PPO in higher plants and microorganisms is not yet known with certainty. Intensive efforts to show that it is involved in photosynthesis and/or energy induction have failed to date. The action of PPO leads to major economic losses in some fresh fruits and vegetables, such as Irish potatoes, lettuce and some other leafy vegetables, apples, apricots, bananas, grapes, peaches and strawberries (2). In some tropical fresh fruits, up to 50% can be lost due to the enzyme-caused browning. Browning also leads to off- flavors and losses in nutritional quality. Therefore, the consumer will not select fruits 0097H5156/95/0600-0002$12.00/0 © 1995 American Chemical Society Downloaded by 27.96.103.238 on May 13, 2015 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0600.ch001 In Enzymatic Browning and Its Prevention; Lee, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.